With force measuring devices frequently there is the problem that due to tolerances or temperature expansion, respectively, of the load introducing elements or the base, and due to variations in loading or a lateral influence, as by wind squalls or the like, the force measuring device is considerably affected outside the desired vertical force direction.
For example, FIG. 32 shows a bin 70 supported on a base 72 by force measuring devices 110 and corresponding supports 74. The force measuring devices 110 are loaded through lateral flanges 78 of bin 70. Depending on the extent bin 70 is filled, bending of flanges 78 may occur which may vary plan parallelism in the force measuring devices 110. Due to temperature expansion the distance between the central axes of force measuring devices 110 at the force introduction side may considerably be displaced in respect of the support side. Heavy side winds result in a tilting of bin 70 about a horizontal axis, again influencing the plan parallelism in force measuring devices 110, in addition to usual variations thereof. Furthermore, a twisting about a vertical axis is difficult to avoid. Therefore, specific measures must be taken ensuring the necessary degrees of freedom of movement without affecting the force measuring device in its measuring accuracy or even destroying it.
U.S. Pat. No. 4,754,653 discloses a force measuring device comprising as a force introducing element a piston inserted into a relatively high cylindrical recess of a pot-type housing forming a narrow annular gap filled with elastomeric material fixedly adhering to the contact surfaces. Through further elastomeric material the piston acts on a pressure sensor. The elastomeric material completely transmits the vertical force component to the pressure sensor, whilst lateral force components are shunted from the piston through the elastomeric material in the annular gap to the pot-type housing. This known force measuring device has a relatively high measuring accuracy; however, its manufacture is relatively expensive and its mounting is complex, if the influences mentioned above are to be avoided.
German Patent Application Publication No. 21 06 92 discloses a force measuring cell comprising a cube-type block of elastomeric material sandwiched between two plates and having a pressure sensor embedded therein. Such a force measuring device is relatively inaccurate, since upon force application the elastomeric block expands laterally causing a considerable hysteresis and non-linearity of the measuring results. Instead of the elastomeric block disc-type discrete bodies of different pressure stability may be stacked in a telescopic tube body, the discrete bodies being destroyed at a different loading each.
U.S. Pat. No. 4,466,297 discloses a force measuring device featuring a force transmission by a wedge arrangement with the wedge being supported by a cushion. The cushion may comprise a ring made of sandwiched layers of elastomeric material and metal and enclosing a liquid space. Therefore, there is no uniform elastomeric block.
The force measuring device according to German Patent Application Publication No. 35 02 275 comprises a pot having inserted therein an elastomeric cushion having included therein a pressure measuring cell and being loaded by a piston.
U.S. Pat. No. 4,770,050 relates to a pressure measuring cell with the pressure being transmitted to a pressure sensor through elastomeric material filled into a pot-type housing.
U.S. Pat. No. 4,739,666 relates to a force measuring device including a pot-type base body having a piston inserted therein, with elastomeric material being provided between the end surface of the piston and the bottom of the base body, the elastomeric material being in contact with at least one pressure sensor. The base body is supported by a pot bearing provided at its bottom side and including an elastomeric plate.
German Patent Application Publication No. 21 58 607 relates to a force measuring cell comprising spaces filled with liquid and peripherally enclosed by resilient elements. Force introduction is accomplished through a stiff center of the resilient elements which elements are formed in a sandwich-type manner.
German Patent Application Publication No. 29 17 363 discloses a force measuring device including a body being elastic along its length and form-stable over its cross section. It contains a liquid flowing through a duct to a pressure sensor.